An arrester (sometimes called a lightning arrester or a surge arrester) is a device used on electrical power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning and other fault currents. A typical arrester has a high-voltage terminal and a secondary terminal. When a power surge (fault current) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth (ground, also called an electrical ground or an earth ground). If protection from the arrester fails or is absent, a power surge on the electrical system can introduce thousands of kilovolts that may damage transmission lines and/or cause severe damage to transformers and other electrical or electronic devices.